"Single node" mode should move itself to up and signal this event?

Perhaps one wants to run sometimes in single node mode, and not have to change any initialization code; i.e. code which wants to run "singleton always on leader" may not really care that we are not clustered yet would want to always wait until it receives an .up signal for booting up.

Proposal:

- when running without clustering, not bound to ports, immediately signal self node -> `up` move.
- This can be done synchronously during system startup even

Start by tracing the single-node startup path and the node state transition that emits the `up` event. Confirm how unclustered mode is initialized and whether startup can signal the node synchronously; done means singleton code receives the same `up` signal without changing initialization code.

Written by the indexing model from the issue text.